In relational database management systems, information is stored in tables where each piece of data is stored at a particular row and column. In general, all of the information in a given row is associated with a particular object, and all of the information in a given column relates to a particular category of information. For example, each row of a table may correspond to a particular employee, and the various columns of the table may correspond to employee names, employee social security numbers, and employee salaries.
A user retrieves information from and updates a database by submitting queries to a database management system (DBMS). The DBMS processes the queries by retrieving the information and performing the updates specified in the queries. A transaction is a unit of work that is performed within a DBMS. Each unit of work performed in a database must either complete in its entirety or have no effect whatsoever. Thus, a partial completion of a transaction is not possible. A transaction typically includes a series of queries or statements submitted to the DBMS for sequential execution.